{smcl}
{* 09jul2020}{...}
{cmd:help mata mm_freq()}
{hline}

{title:Title}

{p 4 14 2}
{bf:mm_freq() -- Compute frequency counts}

{title:Syntax}

{p 8 23 2}
{it:real colvector}
{cmd:mm_freq(}{it:x} [{cmd:,} {it:w}{cmd:,} {it:levels}]{cmd:)}

{p 8 23 2}
{it:real colvector}
{cmd:_mm_freq(}{it:x} [{cmd:,} {it:w}{cmd:,} {it:levels}]{cmd:)}

{p 8 23 2}
{it:real colvector}
{cmd:mm_freq2(}{it:x} [{cmd:,} {it:w}]{cmd:)}

{p 8 23 2}
{it:real colvector}
{cmd:_mm_freq2(}{it:x} [{cmd:,} {it:w}]{cmd:)}

{pstd}
where

{p 12 16 2}
{it:x}:  {it:transmorphic matrix} containing data, rows are observations 

{p 12 16 2}
{it:w}:  {it:real colvector} containing weights

{p 7 16 2}
{it:levels}:  {it:transmorphic matrix} containing levels of data, in ascending order


{title:Description}

{pstd}
{cmd:mm_freq()} returns the frequency counts of the "levels" (unique
rows) of {it:x}. That is, {cmd:mm_freq()} computes the
frequency distribution of {it:x}. The frequency counts are returned
in ascending sort order of the levels of {it:x}.

{pstd}
{it:w} specifies weights associated with
the observations in {it:x}. Omit {it:w}, or specify {it:w} as 1 to obtain
unweighted results.

{pstd}{it:levels} specifies the levels
to be counted. {it:levels} must be sorted in ascending order. If
{it:levels} is omitted, {cmd:mm_freq()} determines the frequency counts
of all levels of {it:x}. Furthermore, {it:levels}==. indicates to
determine the counts of all levels and, additionally, return the
levels of {it:x} in {it:levels}.

{pstd}
{cmd:mm_freq2()} returns for each row of {it:x} the 
number of duplicates in {it:x} (or the sum of weights 
associated with the duplicates, respectively). 

{pstd}
{cmd:_mm_freq()} and {cmd:_mm_freq2()} are like {cmd:mm_freq()} and {cmd:mm_freq2()},
but assume that {it:x} is sorted.


{title:Remarks}

{pstd} Example:

        {com}: x = (1\2\3\.\1\3\1\1\2\3\.)
        {res}
        {com}: mm_freq(x,1)
        {res}       {txt}1
            {c TLC}{hline 5}{c TRC}
          1 {c |}  {res}4{txt}  {c |}
          2 {c |}  {res}2{txt}  {c |}
          3 {c |}  {res}3{txt}  {c |}
          4 {c |}  {res}2{txt}  {c |}
            {c BLC}{hline 5}{c BRC}{txt}

        {com}: x, mm_freq2(x,1)
        {res}        {txt}1   2
             {c TLC}{hline 9}{c TRC}
           1 {c |}  {res}1   4{txt}  {c |}
           2 {c |}  {res}2   2{txt}  {c |}
           3 {c |}  {res}3   3{txt}  {c |}
           4 {c |}  {res}.   2{txt}  {c |}
           5 {c |}  {res}1   4{txt}  {c |}
           6 {c |}  {res}3   3{txt}  {c |}
           7 {c |}  {res}1   4{txt}  {c |}
           8 {c |}  {res}1   4{txt}  {c |}
           9 {c |}  {res}2   2{txt}  {c |}
          10 {c |}  {res}3   3{txt}  {c |}
          11 {c |}  {res}.   2{txt}  {c |}
             {c BLC}{hline 9}{c BRC}

        {com}: l = (0\1\2)
        {res}
        {com}: f = mm_freq(x,1,l)
        {res}
        {com}: l, f
        {res}       {txt}1   2
            {c TLC}{hline 9}{c TRC}
          1 {c |}  {res}0   0{txt}  {c |}
          2 {c |}  {res}1   4{txt}  {c |}
          3 {c |}  {res}2   2{txt}  {c |}
            {c BLC}{hline 9}{c BRC}{txt}

{pstd}Note that

        {com}: f = mm_freq(x,1,l=.)
        {res}
        {com}: l, f
        {res}       {txt}1   2
            {c TLC}{hline 9}{c TRC}
          1 {c |}  {res}1   4{txt}  {c |}
          2 {c |}  {res}2   2{txt}  {c |}
          3 {c |}  {res}3   3{txt}  {c |}
          4 {c |}  {res}.   2{txt}  {c |}
            {c BLC}{hline 9}{c BRC}{txt}

{pstd}is equivalent to

        {com}: l = uniqrows(x)
        {res}
        {com}: f = mm_freq(x,1,l)
        {res}
        {com}: l,f
        {res}       {txt}1   2
            {c TLC}{hline 9}{c TRC}
          1 {c |}  {res}1   4{txt}  {c |}
          2 {c |}  {res}2   2{txt}  {c |}
          3 {c |}  {res}3   3{txt}  {c |}
          4 {c |}  {res}.   2{txt}  {c |}
            {c BLC}{hline 9}{c BRC}{txt}

{pstd}Furthermore, {cmd:mm_freq()} may also be used with strings:

        {com}: s = ("a"\"b"\"c"\"b")
        {res}
        {com}: mm_freq(s,1)
        {res}       {txt}1
            {c TLC}{hline 5}{c TRC}
          1 {c |}  {res}1{txt}  {c |}
          2 {c |}  {res}2{txt}  {c |}
          3 {c |}  {res}1{txt}  {c |}
            {c BLC}{hline 5}{c BRC}{txt}


{title:Conformability}

    {cmd:mm_freq(}{it:x}{cmd:,} {it:w}{cmd:,} {it:levels}{cmd:)}, {cmd:_mm_freq(}{it:x}{cmd:,} {it:w}{cmd:,} {it:levels}{cmd:)}:
         {it:x}:  {it:n x c} 
         {it:w}:  {it:n x} 1 or 1 {it:x} 1
    {it:levels}:  {it:l x c} or {it:levels}==.
    {it:result}:  {it:l x} 1.

    {cmd:mm_freq2(}{it:x}{cmd:,} {it:w}{cmd:)}, {cmd:_mm_freq2(}{it:x}{cmd:,} {it:w}{cmd:)}:
         {it:x}:  {it:n x c}
         {it:w}:  {it:n x} 1 or 1 {it:x} 1
    {it:result}:  {it:n x} 1.
    

{title:Diagnostics}

{p 4 4 2}None.


{title:Source code}

{p 4 4 2}
{help moremata_source##mm_freq:mm_freq.mata}


{title:Author}

{p 4 4 2} Ben Jann, University of Bern, jann@soz.unibe.ch


{title:Also see}

{p 4 13 2}
Online:  help for
{bf:{help mf_uniqrows:[M-5] uniqrows()}},
{bf:{help m4_utility:[M-4] utility}},
{bf:{help moremata}}
{p_end}
